Method and Apparatus for Measuring Gas Flow

Abstract

There are described a method and an apparatus for measuring gas flow rate and/or volume (such as gas accumulation and consumption) based on the “rate of rise” method, particularly useful in the field of small gas flow rates, that uses a duct immersed in a liquid so as to generate a hydrostatic pressure that allows increase in pressure in a sealed chamber, so as to avoid the use of solenoid valves, producing a particular advantage when a multiple measurement system is required, when a plurality of gas flows are to be measured. The method can be applied advantageously to measure flow rates of gas produced by chemical and/or biological reactions, in particular the Biochemical Methane Potential (BMP) or the Biochemical Hydrogen Potential (BHP). A variant of the method also allows measurement of the Biochemical Oxygen Demand (BOD).

1 - 17 . (canceled) 
     
     
         18 . A method for measuring a gas flow rate of a gas introduced in a sealed chamber having a volume maintained at a temperature, the method comprising:
 (a) discharging a gas flow from said sealed chamber through a duct immersed in a liquid contained in an ejection cell, said duct having a downward portion, a maximum hydrostatic pressure defined for said gas at a bottom of the downward portion, and an upward portion with an open end, a minimum hydrostatic pressure defined for said gas in correspondence with the open end of the upward portion, said open end being placed below a level of said liquid;   (b) after step (a), passing the gas flow through the bottom of the downward portion at the maximum hydrostatic pressure and moving the gas flow to the upward portion such that the gas flow is ejected from said open end into said liquid, moving the gas flow up to a surface of said liquid into the space above the level of said liquid and then moving the gas flow outside of said ejection cell;   (c) measuring an absolute pressure of said sealed chamber over time, said absolute pressure varying from a minimum pressure, corresponding to the minimum hydrostatic pressure to a maximum pressure, corresponding to the maximum hydrostatic pressure of said gas;   (d) calculating a volume of the gas at standard conditions accumulated in said sealed chamber, corresponding to the absolute pressure, with an ideal gas law equation and calculating the gas flow rate by carrying out a linear interpolation of the volume of gas at standard conditions over time, an angular coefficient of a linear interpolant being an estimate of the gas flow rate; and   (e) repeating steps (a), (b), (c) and (d) a plurality of times, thereby generating a series of compression and ejection steps of said gas and a series of values of parameters of ideal gases equations, obtaining a mean value from the series of values of parameters, such that an accurate measurement of said gas flow rate is obtained in a case of a constant flow rate, or such that a continuous monitoring is carried out in a case of a non-constant flow rate.   
     
     
         19 . The method according to  claim 18 , wherein gas flow rates below 1 L/min in standard conditions are measured. 
     
     
         20 . The method according to  claim 18 , wherein gas flow rates below 0.5 L/min in standard conditions are measured. 
     
     
         21 . The method according to  claim 18 , wherein said maximum hydrostatic pressure in said duct is less than 0.025 atm. 
     
     
         22 . The method according to  claim 18 , wherein said maximum hydrostatic pressure in said duct is less than 0.015 atm. 
     
     
         23 . The method according to  claim 18 , wherein the gas introduced in the sealed chamber is produced in the sealed chamber by at least one of a chemical reaction and a biological reaction. 
     
     
         24 . The method according to  claim 18 , further comprising measuring a biochemical potential of methane production or a biochemical potential of hydrogen production. 
     
     
         25 . The method according to  claim 18 , further comprising measuring a biochemical oxygen demand of a sample. 
     
     
         26 . A gas flow rate measurement apparatus comprising:
 a sealed chamber having a volume, the sealed chamber defining a discharge hole for discharge of a gas flow;   an ejection cell of said gas flow, the ejection cell configured to be partially filled with a liquid;   an ejection duct of said gas flow, connected by one end to said discharge hole of said sealed chamber and having an end portion configured to be immersed in said liquid of said ejection cell, said end portion of said duct shaped with a downward portion and an upward portion with an open end, said open end located below a level of said liquid, whereby said gas flow may be ejected through said duct in said liquid;   pressure and temperature sensors configured to detect an absolute pressure and a temperature in at least one of the sealed chamber and the ejection cell; and   a temperature-controlled section at least partially surrounding one or more of the sealed chamber and the ejection cell.   
     
     
         27 . The apparatus according to  claim 26 , wherein said sealed chamber is provided with two holes, a first hole for the introduction of a gas flow and a second hole for the discharge of the gas flow. 
     
     
         28 . The apparatus according to  claim 26 , wherein said sealed chamber is provided with a single hole for the discharge of the gas flow, the sealed chamber being a reaction chamber within which said gas flow is produced by chemical and/or biological reactions. 
     
     
         29 . The apparatus according to  claim 28 , wherein:
 one or more of the sealed chamber and the ejection cell are placed in a thermostatic bath or in a controlled temperature chamber; and   the sealed chamber is equipped with a mixing system.   
     
     
         30 . The apparatus according to  claim 29 , wherein at least one of a supply line of reagents and a sample line of product gas is connected to the sealed chamber. 
     
     
         31 . The apparatus according to  claim 26 , wherein said downward portion and said upward portion of said ejection duct are parallel. 
     
     
         32 . The apparatus according to  claim 26 , wherein an internal diameter of said ejection duct is less than 25 mm. 
     
     
         33 . The apparatus according to  claim 26 , wherein an internal diameter of said ejection duct is less than 10 mm. 
     
     
         34 . The apparatus according to  claim 26 , wherein said ejection duct is made with one or more terminals notches on said open end or in the proximity of said open end, the terminal notches configured to allow re-establishment of starting conditions of a cycle in a spontaneous way, whereby continuous and subsequent steps of compression and ejection are performed. 
     
     
         35 . The apparatus according to  claim 26 , further comprising:
 a biological reactor connected to said chamber by a duct;   at least one sensor configured to measure a biochemical potential of methane production in the a head space of the sealed chamber; and   wherein the temperature-controlled section includes a thermostatic bath or a temperature controlled chamber.   
     
     
         36 . The apparatus according to  claim 35 , wherein said sealed chamber is partially filled with an alkaline solution with a CO 2  absorbing function, and said biological reactor is equipped with a mixing system. 
     
     
         37 . The apparatus according to  claim 36 , wherein said biological reactor is further equipped with one or more supply/sampling lines of at least one of reagents and product gas. 
     
     
         38 . A method to measure consumption of a gas, the method comprising:
 (a) consuming a gas flow in a sealed reaction chamber, the chamber including a volume maintained at a temperature, by at least one of a chemical reaction and a biological reaction taking place in said chamber, said sealed chamber being connected to a closed flow-back cell in which said gas to be consumed is present, such that decreasing a pressure in said flow-back cell occurs resulting from the consumption of the gas in said sealed chamber;   (b) withdrawing said gas flow by said flow-back cell from a constant pressure storage chamber and transferring the gas flow into said flow-back cell via a duct immersed in a liquid contained in said flow-back cell, said duct having a downward portion, a maximum negative hydrostatic pressure for said gas defined at a bottom of the downward portion, and an upward portion ending with an open end, a minimum negative hydrostatic pressure for said gas defined in correspondence with the open end, said open end being placed below a level of said liquid;   (c) discharging said gas flow from said storage chamber through said duct, the gas flow passing the bottom of the downward portion at the maximum negative hydrostatic pressure and moving to the upward portion such that the gas flow is ejected from said open end into said liquid, the gas flow moving to a surface of said liquid and into a space above the level of said liquid, the space in connection with said sealed chamber in which the at least one of the chemical reaction and the biological reaction takes place, such that the starting pressure conditions are re-established;   (d) measuring an absolute pressure of said sealed chamber over time, said absolute pressure varying from a minimum pressure corresponding to the minimum negative hydrostatic pressure, to a maximum pressure, corresponding to the maximum negative hydrostatic pressure of said gas;   (e) calculating a volume of gas at standard conditions accumulated in the sealed chamber, corresponding to the absolute pressure, with an ideal gas law equation and calculating a gas flow rate by carrying out a linear interpolation of the volume of gas at standard conditions over time, an angular coefficient of a linear interpolant being an estimate of the gas flow rate; and   (f) repeating steps (a), (b), (c), (d) and (e) a plurality of times to generate a series of steps creating a negative pressure and re-establishing a starting pressure of said gas, and creating a series of values of parameters of the ideal gas law equation from which a mean value is obtained, such that an accurate measurement of said gas flow rate is obtained in the case of a constant flow rate, or such that a continuous monitoring is carried out in the case of a non-constant flow rate.   
     
     
         39 . A gas flow measurement apparatus for measuring consumption of a gas by at least one of a chemical reaction and a biological reaction, the gas flow measurement apparatus comprising:
 a sealed reaction chamber including a volume and a hole defined in the sealed reaction chamber for introduction of a gas flow to be consumed in said sealed reaction chamber;   a flow-back cell of said gas flow, the flow-back cell configured to contain a liquid which fills a part of said cell and a volume portion defined above a level of said liquid, the volume portion configured to contain said gas and in connection with said sealed reaction chamber;   a flow-back duct mounted in said flow-back cell, the flow-back duct having a terminal part immersed in said liquid and shaped with a downward portion and an upward portion, an open end of the flow-back duct placed below the level of said liquid, whereby said gas can be transferred from said duct into said liquid and from the liquid into said volume portion above said liquid;   said flow-back duct connected at an end opposite the open end to a constant pressure storage chamber containing said gas to be consumed in said sealed reaction chamber;   at least one pressure sensor configured to measure absolute pressure in one or more of the sealed reaction chamber, the flow-back cell, and the storage chamber;   at least one temperature sensor configured to measure temperature in one or more of the sealed reaction chamber, the flow-back cell, and the storage chamber; and   a temperature-controlled section at least partially surrounding one or more of the sealed reaction chamber, the flow-back cell, and the storage chamber.   
     
     
         40 . The apparatus according to  claim 39 , wherein said flow-back duct includes one or more terminals notches defined on the open end or in the proximity of said open end, the terminal notches configured to allow re-establishment of starting conditions of a cycle in a spontaneous way, whereby continuous and subsequent steps of compression and ejection are performed.